This proposal has two main objectives. First we will explore in detail those properties of the cyclic AMP system which are common to cultured epithelial cells. Secondly we will compare the cyclic AMP metabolism of normal and neoplastic epithelial cells, and explore the relevancy of abberations in its metabolism to the establishment for perpetuation of the malignant state. During the first year and a half of this project we have observed that cultured epithelial cells exhibit both homologous and heterologous refractoriness with respect to the ability of beta adrenergic agonists to stimulate the accumulation of intracellular cyclic AMP. Our results suggest that beta adrenergic refractoriness in epithelial cells is a complex phenomenon involving both homologous and heterologous agents as well as cyclic AMP dependent and independent mechanisms. We have also found evidence for the presence of soluble inhibitors of cyclic nucleotide phosphodiesterase and cultured epithelial cells. The inhibitor has been separated from phosphodiesterase and partially purified by blue dextran affinity chromatography. The inhibitor was found to be non-dialyzable, inactivated by trypsin and boiling, but stable to a 60 degrees C, 30 min. heat treatment. Both calcium dependent and calcium independent forms of PDE were inactivated by the inhibitor. In comparing normal and chemically transformed epithelial cells we have found that the chemically transformed cells produced 20 fold more cyclic AMP when challenged with cholera toxin than their normal counterparts. We have also found that cholera toxin induces drastic morphological change in chemically transformed epithelial cells but no such change occurs in the normal counterparts.